The present invention relates to pump, and more particularly to an improved pumping apparatus suitable for pumping plastic concrete, such as low or even zero slump concrete, and other similar materials and mixtures.
One common application for such a pumping apparatus is to pump plastic concrete to elevated levels, such as to the upper stories of a building being constructed, or to pump plastic concrete to other points which are inaccessible to trucks. Heretofore, various pumping devices have been devised to pump unset plastic concrete to remote locations. Most commercial forms of these pumps depend on gravity head and pressure differential for charging. As a consequence, they are unsuitable for use in pumping zero slump concrete and other similar mixes since zero slump concrete has a low water-cement ratio and generally will not flow under the influence of either gravity head or pressure differential. Thus, these prior art pumps are incapable of pumping zero slump concrete since the pump will not charge.
Other types of pumping apparatus, however, have been devised which have employed both fixed and sliding sleeves or cylinders and through which pistons are advanced to eject and thereby pump the plastic concrete. These pumping apparatuses have generally included a valve to control the flow of concrete through their discharge outlet, such a valve being necessary in operations where concrete is being pumped to an elevated location in order to prevent the backflow of concrete through the discharge hose between work strokes of the pumping mechanism.
Heretofore, the valves in these pumping apparatuses have generally been plagued by the problems of wear, mix separation and admission of air. Mix separation is the separation of the mix ingredients in the concrete being pumped and occurs whenever the pump valve does not completely close, i.e., remains partially open. When the valve fails to completely close, the mortar phase of the concrete mix tends to backflow into the pump with the result that a relatively dry pocket of coarse aggregate, a so called rock pocket, is formed in the discharge hose adjacent the valve. As the concrete is then pumped through the discharge hose, these rock pockets do not as readily flow through the discharge hose since they are not sufficiently surrounded by the mortar to be adequately lubricated. Thus, the formation of rock pockets in the pump discharge line has the disadvantage of significantly increasing discharge line pressure with the result that the pumping apparatus is subjected to increased strain and wear.
Another disadvantage inherent with partially open valves is that the valve parts are rapidly eroded by the mortar phase passing therethrough during the occurrence of mix separation. Such erosion increases the valve opening and as the valve opening increases, erosion and wear increase, with the result that the wear rate of the valve is not constant, but rather increases rapidly with use.
In order to avoid the problems of mix separation and increased wear rate, attempts have been made to design pump valves which close completely. Unfortunately, such prior art valves tend to crush rock during their operation and this rock crushing causes the valves to wear very rapidly. Due to the rapid wear caused by the crushing of the rock, these prior valves in a short time are generally worn to such extent as to no longer fully close. Once the valves no longer fully close, they then function the same as the partially open valves above described, and consequently have the above-mentioned drawback of having a wear rate which increases with use and also the drawback of causing mix separation.
Prior art concrete pumping systems have also generally been susceptible to the admission of air at their valve seals during pumping operations. The admission of air, in addition to reducing the volumetric efficiency of the pumping operation, also causes undesirable surge effects in the pump discharge line due to the presence of the admitted air therein. Also, prior art valves, which as abovementioned are generally subjected to considerable wear by the rough concrete mixtures they pump, have often not been designed for ready disassembly, repair and replacement of worn parts.